Field of the Application
The present invention relates to a control apparatus for a vehicle including an engine with a turbocharger that is capable of lean-burn operation, and an automatic transmission.
Background Art
As disclosed in Japanese Patent Laid-Open No. 2013-119832, an engine with a turbocharger that is capable of lean-burn operation is known as an engine for a vehicle. Lean-burn operation can be performed in both a supercharging region in which supercharging is performed by a turbocharger, and a natural aspiration region in which supercharging is not performed. Hereunder, an operation mode of an engine that performs lean-burn operation in a supercharging region is referred to as a “supercharged lean-burn operation mode”, and an operation mode of an engine that performs lean-burn operation in a natural aspiration region is referred to as a “natural aspiration lean-burn operation mode”.
Other prior art includes Japanese Patent Laid-Open No. 2002-106703.
In a vehicle equipped with the above described engine, selection of an operation mode of the engine is performed in accordance with the engine output that a driver requests. For example, the natural aspiration lean-burn operation mode is selected when the driver requests a small engine output, such as when travelling at a low speed. Subsequently, when accelerating from the state in which the vehicle is travelling at a low speed, a transition from the natural aspiration lean-burn operation mode to the supercharged lean-burn operation mode is performed to increase the engine torque in accordance with an increase in the engine output requested by the driver.
In this connection, during lean-burn operation the energy (referred to as “exhaust energy”) of exhaust gas is less than during stoichiometric-burn operation, and the rotational speed of a turbine does not rapidly increase even when a supercharging region has been entered. Consequently, when transitioning from the natural aspiration lean-burn operation mode to the supercharged lean-burn operation mode, a delay arises with respect to an increase in the intake pipe pressure, and due to a torque response delay (that is, a delay in the response of the actual torque with respect to the target torque) that arises accompanying the aforementioned delay, there is a risk of fluctuations or discontinuities arising in the engine output. Fluctuations or discontinuities in the engine output cause a deterioration in the drivability of the vehicle.